Capacitive probe structure for testing the integrity of electrical cables and conductors

Claim 2

A probe structure designed to be capacitively coupled to an insulated electrical conductor installed in the field without damage to the insulation, said probe structure being operative to pick up through said insulation electrical signals induced on or carried by a selected internal part of the conductor and convert signals having high input impedance into stable signals capable of audible or scientific measurement; said probe structure including a sIgnal pickup plate formed of conductive material designed to be capacitively coupled to the conductor, a shielding plate formed of conductive material extending parallel to and positioned below and having a larger area than said signal pickup plate, the underface of said shielding plate being bonded to a head block formed of nonconductive material and the upper face of said shielding plate being bonded to the superimposed signal pickup plate by an intermediate layer of insulating plastic, a protective facing of wear resistant and nonconductive material covering the upper face of said signal pickup plate and all surrounding areas of said shielding plate and head block; a base box supporting said head block, electronic components forming a unity gain high input impedance converting circuit contained in said base box and positioned adjacent to the underside of said head block, and a pair of electrical connectors extending through said head block and respectively electrically connecting said signal pickup plate and said shielding plate to said impedance converting circuit.

Claim 3

A probe structure as specified in claim 1 characterized by a V-shaped facing layer whose side faces are inclined to each other at an angle in the order of 90* to 150*.

Claim 4

A probe structure as specified in claim 1 and wherein said protective layer, signal pickup plate, intermediate plastic layer, shielding plate and plastic head block are compactly assembled as an integral unit by heat and pressure.

Claim 5

A probe structure designed to be capacitively coupled to an insulated electrical conductor installed in the field without damage to the insulation, said probe structure being operative to pick up through said insulation electrical signals induced on or carried by a selected internal part of the conductor and convert signals having high input impedance into stable output signals capable of audible or scientific measurement; said probe structure including a V-shaped signal pickup plate formed of conductive material designed to be capacitively coupled to said conductor, a V-shaped shielding plate formed of conductive material extending parallel to and positioned below said signal pickup plate and having a larger area than said signal pickup plate, the underface of said shielding plate being bonded to the upper face of a head block formed of nonconductive plastic, an intermediate bonding layer of nonconductive plastic sandwiched between said shielding plate and signal pickup plate, a protective facing layer of wear resistant and nonconductive material covering said signal pickup plate and all surrounding areas of said shielding plate and head block, a base box supporting said head block, a printed circuit board contained in said base box and suspended from and adjacent to the underside of said head block, electronic components forming a unity gain high input impedance converting circuit contained in said base box and supported by said circuit board, and a pair of electrical leads extending through said head block and respectively electrically connecting said signal pickup plate and said shielding plate to said impedance converting circuit.

Claim 6

A probe structure designed to be capacitively coupled to an insulated electrical conductor installed in the field without damage to the insulation, said probe structure being operative to pick up through said insulation electrical signals induced on or carried by a selected internal part of the conductor and convert signals having high input impedance into stable output signals capable of audible or scientific measurement; said probe structure including a V-shaped signal pickup plate formed of conductive material designed to be capacitively coupled to said conductor, a V-shaped shielding plate formed of conductive material extending parallel to and positioned below said signal pickup plate and having a larger area than said signal pickup plate, the underface of said shielding plate being bonded to the upper face of a head block formed of nonconductive plastic, an intermediate bonding layer of nonconductive plastic sandwiched between said shielding plate and signal pickup plate, a protective facing layer of wear resistant and nonconductive material covering said signal pickup plate and all surrounding areas of said shielding plate and head block, a base box supporting said head block, a printed circuit board contained in said base box and suspended from and adjacent to the underside of said head block, electronic components forming a unity gain high input impedance converting circuit contained in said base box and supported by said circuit board, and a pair of electrical leads extending through said head block and respectively electrically connecting said signal pickup plate and said shielding plate to said impedance converting circuit.

Claim 7

A probe structure as defined in claim 4 and wherein said high impedance converting circuit includes a field effect transistor whose gate is connected to said pickup electrode and whose source is connected to the noninverting input of a unity gain voltage follower, said unity gain voltage follower having a low output impedance terminal, said low output impedance terminal being connected to the inverting input of said unity gain voltage follower and to said shielding electrode to thereby provide a driven shield.

Claim 8

A probe structure as defined in claim 4 and wherein said impedance converting circuit embraces a voltage follower device having a high impedance signal input terminal connected to said pickup electrode, a direct current power input terminal, and a signal output terminal, a second voltage follower having its input terminal connected tO the output terminal of said first voltage follower device and a low impedance output terminal connected to said shielding electrode, and means for coupling signal frequency potentials from the output of said second voltage follower device to the power input terminal of said first voltage follower device.

Claim 9

A probe structure for evaluating the integrity of the shielding of an insulated and shielded communication cable installed in the field and without damage to the insulation, said probe structure including; a head block formed from nonconducting plastic and presenting a V-shaped upper face bonded to a V-shaped shielding electrode, a V-shaped pickup electrode of smaller area than said shielding electrode and bonded to said shielding electrode by an intermediate nonconductive plastic layer, and a facing layer formed of wear resistant and nonconductive plastic covering and bonded to said pickup electrode and the surrounding areas of said shielding electrode and plastic head block; a base box supporting said head block, a circuit board contained within said base box and suspended from the underside of the head block, electronic components forming a high impedance converting circuit mounted on said circuit board and embracing an operational amplifier of voltage follower configuration having a noninverting input terminal connected to the said pickup electrode and an output terminal connected to the inverting input terminal of said amplifier and to said shielding electrode plate to thereby provide a driven shield.

Claim 10

A probe structure for evaluating the integrity of the shielding of an insulated and shielded communication cable installed in the field and without damage to the insulation, said probe structure including; a head block formed from nonconducting plastic and presenting a V-shaped upper face bonded to a V-shaped shielding electrode, a V-shaped pickup electrode of smaller area than said shielding electrode and bonded to said shielding electrode by an intermediate nonconductive plastic layer, and a facing layer formed of wear resistant and nonconductive plastic covering and bonded to said pickup electrode and the surrounding areas of said shielding electrode and plastic head block; a base box supporting said head block, a circuit board contained within said base box and suspended from the underside of the head block, electronic components forming a high impedance converting circuit mounted on said circuit board and embracing an operational amplifier of voltage follower configuration having a noninverting input terminal connected to the said pickup electrode and an output terminal connected to the inverting input terminal of said amplifier and to said shielding electrode plate to thereby provide a driven shield.

Claim 11

A probe structure as defined in claim 7 which further includes a handpiece member, and means for adjustably connecting one end of said handpiece member to said base box and whereby said base box may be frictionally adjusted to place the pickup electrode plate firmly against the insulated cable whose shielding integrity is to be evaluated.

Claim 12

A probe structure for evaluating the integrity of the shielding of an insulated and shielded communication cable installed in the field and without damage to the insulation, said probe structure including; a head block formed from nonconducting plastic and presenting a V-shaped upper face bonded to a V-shaped shielding electrode, a V-shaped pickup electrode of smaller area than said shielding electrode and bonded together by an intermediate nonconductive plastic layer, and a facing layer formed of wear resistant and nonconductive material covering and bonded to said pickup electrode and the surrounding areas of said shielding electrode and plastic head block; a base box supporting said head block, and a unity gain high impedance converting circuit contained in said base box and positioned adjacent to the underside of said head block, said high impedance converting circuit embracing the combination of a field effect transistor whose gate is connected to said pickup electrode, and an integrated circuit unity gain voltage follower, the output of said transistor being connected to the noninverting input of said voltage follower and the output of said voltage follower being connected to the inverting input of said voltage follower and to the shielding electrode to thereby provide a driven shield.

Claim 13

A probe structure for evaluating the integrity of the shielding of an insulated and shielded communication cable installed in the field and without damage to the insulation, said probe structure including; a head block formed from nonconducting plastic and presenting a V-shaped upper face bonded to a V-shaped shielding electrode, a V-shaped pickup electrode of smaller area than said shielding electrode and bonded together by an intermediate nonconductive plastic layer, and a facing layer formed of wear resistant and nonconductive material covering and bonded to said pickup electrode and the surrounding areas of said shielding electrode and plastic head block; a base box supporting said head block, and a unity gain high impedance converting circuit contained in said base box and positioned adjacent to the underside of said head block, said high impedance converting circuit embracing the combination of a field effect transistor whose gate is connected to said pickup electrode, and an integrated circuit unity gain voltage follower, the output of said transistor being connected to the noninverting input of said voltage follower and the output of said voltage follower being connected to the inverting input of said voltage follower and to the shielding electrode to thereby provide a driven shield.

Claim 14

A probe structure as defined in claim 9 which further includes a positive direct current source connected to said voltage follower and through a first resistor to the drain terminal of said transistor; and a negative direct current source connected to said voltage follower and through a second resistor to the output terminal of said transistor.

Claim 15

A probe structure as defined in claim 9 which further includes; a positive direct current source connected to said voltage follower and through a first resistor to the drain terminal of said transistor, a negative direct current source connected to said voltage follower and through a second resistor to the output terminal of said transistor; a grounding terminal connected through a third resistor and a first capacitor to the output terminal of said voltage follower, said third resistor being further connected through a fourth resistor to the gate of said transistor, the output terminal of said voltage follower being further connected through a second capacitor to the drain terminal of said transistor.

Claim 16

A probe structure as defined in claim 9 which further includes; a handpiece member, means for adjustably securing one end of said handpiece member to said base box and whereby said base box may be frictionally adjusted to place the pickup electrode firmly against the insulated cable whose shielding integrity is to be evaluated, a crossbar, an adjustable clamp at the other end of said handpiece member for frictionally securing the handpiece member to said crossbar and whereby the pickup electrode may be frictionally held in tilted position to accommodate the position of the cable, a supporting pole connected to the cross-bar, and a bracing member extending from said crossbar and adapted to brace against the cable to facilitate coupling contact between the pickup electrode and the cable.